Magnetization Slow Dynamics in Mononuclear Co(II) Field-Induced Single-Molecule Magnet

Abstract

The novel tridentate ligand L (2,6-bis(1-(n-decyl)-1H-benzimidazol-2-yl)pyridine) was used for the synthesis of mononuclear Co(II) complex 1 with the general formula [Co(L)Br 2 ]. A single-crystal X-ray structural investigation confirmed the expected molecular structure, and noncovalent contacts were inspected by a Hirschfeld surface analysis. The electronic structure of square-pyramidal complex 1 contains an orbitally degenerate ground state which predetermines the use of the Griffith−Figgis Hamiltonian for the analysis of magnetic properties. CASSCF-NEVPT2 calculations and far-infrared magnetic spectroscopy show excellent agreement with the Griffith− Figgis Hamiltonian parameters obtained from the magnetic investigation. The high and negative value of the axial crystal field parameter Δ ax and the calculated g-tensor components suggest the axial magnetic anisotropy of 1. The low-temperature X-band EPR spectra were analyzed within a simplified effective spin-1/2 Hamiltonian to determine effective g-tensor components of the ground Kramers doublet, which agree with the electronic structure predicted within the CASSCF-NEVPT2 theory. An AC magnetic investigation revealed field-supported single-channel slow relaxation of magnetization with maximum relaxation time τ ≈ 28 ms at low temperatures. The comprehensive analysis of the field and temperature evolution of τ indicates that direct, Raman, and Orbach processes are all involved in slow relaxation of magnetization in 1.

Zero-Field SMM Behavior Triggered by Magnetic Exchange Interactions and a Collinear Arrangement of Local Anisotropy Axes in a Linear Co3II Complex

“…Although the GF model was developed for octahedral or axially distorted octahedral complexes (square bipyramid), it has been also successfully applied to square-pyramidal distorted complexes. 31 In this case, the two lowest crystal-field terms derive from the splitting of the 4 T 1g ; therefore, the T–P isomorphism could be applicable. However, for distorted trigonal prismatic and antiprismatic complexes, where the lowest crystal-field terms derive from the 4 E ground term, 8g this choice is more questionable.…”

Neutral cobalt(ii)-bis(benzimidazole)pyridine field-induced single-ion magnets for surface deposition

“…The 4 T 1g LFT is split within the range of 0-3000 cm −1 with the lowest excited state having energy greater than 1800 cm −1 assuring applicability of spin Hamiltonian formalism. 7,14,15 The LFT's are split into ligand-field multiplets (LFM) due to spin-orbit coupling, resulting in ZFS as an energy separation between the two lowest Kramers doublets. The resulting ZFS parameters were found to be very similar for both complexes: D = +25.6 (1) and +25.4 cm −1 (2) and E/D = 0.146 (1), 0.138 (2).…”

“…This type of behavior in magnetic FTIR among similar com- pounds has also been observed in other materials in our previous studies. 7,15 Although we still do not have a satisfactory explanation yet, we are working to understand the influence of the spin-phonon coupling. 39 Indeed, as it will be shown in the dynamic magnetic investigation section, complex 1 has a much faster relaxation than complex 2 and this coincides with the fact that the magnetic peak has a stronger intensity in 1 compared to 2.…”

“…7,14 Our recent reports were focused on the pentacoordinate Co(II)-SIMs with bbp ligands functionalised by long aliphatic chains. 7,15 This modification enables good solubility in non-polar and volatile solvents used for lithographical deposition. Unfortunately, the weak halogenido coordination bonds are likely to have played a role in the thermal instability observed in the reported neutral pentacoordinate Co(II)-SIMs, ultimately hindering their successful surface deposition via sublimation.…”

Influence of the phonon-bottleneck effect and low-energy vibrational modes on the slow spin-phonon relaxation in Kramers-ions-based Cu(ii) and Co(ii) complexes with 4-amino-3,5-bis-(pyridin-2-yl)-1,2,4-triazole and dicyanamide

“…Both approaches suggest the presence of the easy axis anisotropy of the crystal field. Direct estimation of the anisotropy parameters and resulting energy barrier may be performed by high-frequency EPR or, in the case of large energy barriers as in 2 more suitable far-infrared magnetic spectroscopy (FIRMS), 63 which may reveal the spin-phonon coupling with low energy vibrations as well. 64…”